Android Battery Broadcasts

I am trying to make a Battery Alarm Application. I was reading the Android docs and found out that we don't need to register a BroadcastReceiver. We could do something like this-

IntentFilter ifilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
Intent batteryStatus = context.registerReceiver(null, ifilter);

MY QUESTIONS ARE-

• Does the system broadcast intent(containing battery status) every time the battery level change?
• Do I have to query each time for battery level?
• Also, How to play the alarm when the battery level reaches a particular level(set by the user).

here is a full sample to get battery level

private float getBatteryLevel() {
    Intent batteryStatus = registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
    int batteryLevel = -1;
    int batteryScale = 1;
    if (batteryStatus != null) {
      batteryLevel = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, batteryLevel);
      batteryScale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, batteryScale);
    }
    return batteryLevel / (float) batteryScale * 100;
  }

answering your questions:

1- Yes, you can get additional information by getExtra and define the key,BatteryManager has a lot of keys to extract information from the intent.

2- no, you just have to register the reciever and unregister it accoording to the Activity or Fragment lifcycle, usually registering in onCreate()/onCreateView() and unregistering in onDestry()/onDestroyView().

3- you can create a bound service that has a simple notification interface. you register your reciever on it, and from the previous sample you could do something like this:

if (getBatteryLevel < 10) {
//show notification or do whatever you want.
}